Relationships Between Setting Parameter Base Current, Ct Rated Primary Current And Minimum Pickup Of A Protection Ied; Setting Of Voltage Channels; Example - ABB Relion 670 Series Applications Manual

Section 4
Analog inputs
4.2.3 Relationships between setting parameter Base Current, CT rated
primary current and minimum pickup of a protection IED
Note that for all line protection applications (e.g. distance protection or line differential
protection) the parameter Base Current (i.e. IBase setting in the IED) used by the relevant
protection function, shall always be set equal to the largest rated CT primary current among all
CTs involved in the protection scheme. The rated CT primary current value is set as parameter
CTPrim under the IED TRM settings.
For all other protection applications (e.g. generator, shunt reactor, shunt capacitor and
transformer protection) it is typically desirable to set
of the protected object. However this is only recommended to do if the rated current of the
protected object is within the range of 40% to 120% of the selected CT rated primary current. If
for any reason (e.g. high maximum short circuit current) the rated current of the protected object
is less than 40% of the rated CT primary current, it is strongly recommended to set the parameter
IBase in the IED to be equal to the largest rated CT primary current among all CTs involved in the
protection scheme and installed on the same voltage level. This will effectively make the
protection scheme less sensitive; however, such measures are necessary in order to avoid possible
problems with loss of the measurement accuracy in the IED.
Regardless of the applied relationship between the
current, the corresponding minimum pickup of the function on the CT secondary side must always
be verified. It is strongly recommended that the minimum pickup of any instantaneous protection
function (e.g. differential, restricted earth fault, distance, instantaneous overcurrent, etc.) shall
under no circumstances be less than 4% of the used IED CT input rating (i.e. 1A or 5A). This
corresponds to 40mA secondary for IED 1A rated inputs and to 200mA secondary for IED 5A rated
inputs used by the function. This shall be individually verified for all current inputs involved in the
protection scheme.
Note that exceptions from the above 4% rule may be acceptable for very special applications (e.g.
when Multipurpose filter SMAIHPAC is involved in the protection scheme).
4.2.4

Setting of voltage channels

As the IED uses primary system quantities the main VT ratios must be known to the IED. This is
done by setting the two parameters
phase value can be used even if each channel is connected to a phase-to-ground voltage from the
VT.
4.2.4.1

Example

Consider a VT with the following data:
132kV
3
EQUATION1937 V1 EN-US
The following setting should be used:
82
120V
3
IBase parameter equal to the rated current
IBase parameter and the rated CT primary
VTsec and VTprim for each voltage channel. The phase-to-
VTprim=132 (value in kV) VTsec=120 (value in V)
1MRK 511 358-UUS A
GUID-8EB19363-9178-4F04-A6AC-AF0C2F99C5AB v1
SEMOD55055-44 v3
SEMOD55055-47 v2
(Equation 1)
Application manual